An Etymological Dictionary of Astronomy and Astrophysics

The theoretical → low-energy neutrinos that decoupled from the rest of matter about two seconds after the → Big Bang when the temperature dropped to approximately 2.5 MeV (redshift of z ~ 6 ×10⁹). The CNB is similar to the → cosmic microwave background (CMB), but
older. It is estimated that today the CNB has a temperature of T_ν = (4/11)^1/3T_γ, ~ 1.95 K (or 1.67 × 10^-4 eV), where T_γ is the CMB temperature of 2.728 K. Also called the relic neutrinos.

See also: → cosmic; → neutrino; → background.